I'm writing about a setting where the people have some advanced theoretical knowledge, but as yet limited manufacturing ability; in particular, they do not yet have metallurgy, but they are trying to make some fairly complex machines such as spinning wheels, wheelbarrows, pottery wheels and watermills, that require precise moving parts that can withstand significant stress; in our world, these had to wait until they could be made from metal.
But one thing they do have access to is a magical power to shape stone. That eliminates the usual disadvantage of stone for such purposes, that it cannot easily be worked into precise, complex shapes.
There is still the problem that, while some kinds of stone (e.g. flint) are hard and resistant to wear, stone always has poor tensile strength. For some applications, this might be overcome simply by using a sufficient thickness of it, but gears need to fit in the machinery they are driving, and wheels and axles cannot be arbitrarily heavy and still move around.
Given the ability to shape any kind of stone into arbitrarily precise, complex shapes, could the above artifacts be made to work?
My current best guess is that medium-duty things like pottery wheels can work, just by making all the moving parts thick enough to withstand the relatively light stresses placed on them; a pottery wheel doesn't have to withstand forces above a few hundred newtons, I think. But a watermill? It seems to me that the gears connecting the mill to the load it drives, need to withstand enormous force, such that if they were made of stone, the gear teeth would quickly break off; for that application, there is no alternative to using metal, because you need both hardness and tensile strength.
Is that estimate correct, or am I missing something? Is there an easy way to do quantitative estimates for this?